This invention relates to hydraulic fluid systems and, in particular, to hydraulic fluid reservoirs having photodetectors for sensing fluid level and to reservoirs for use with unbalanced hydraulic cylinders.
Hydraulic reservoirs are common components for many hydraulic systems, for example for use in providing pressurized hydraulic fluid to hydraulic cylinders. One problem associated with such systems is ensuring that a proper level of fluid is maintained in the reservoir. One solution to this problem has been placing a photodetector in a position to detect the level of fluid in the reservoir through a transparent or translucent portion of the reservoir. The fluid is colored and this coloration assists the sensor in detecting the presence or absence of fluid within the container and accordingly the level of fluid. However, in practice air frequently becomes entrained in the fluid and causes the color of the fluid to lighten. This may confuse the sensor and may lead to incorrect readings on the level of the fluid within the reservoir.
Another problem associated with hydraulic reservoirs is the necessity in some systems to accommodate differential flows of fluids flowing into the reservoir and flowing out of the reservoir. This may occur, for example, when the reservoir is used in association with an unbalanced hydraulic cylinder. Such cylinders have a higher volume of fluid on the side of the piston opposite the piston rod compared to the side of the piston where the piston rod is located. This means that in one direction of movement of the cylinder, there is more fluid moving towards the cylinder, and out of the reservoir, than there is moving away from the cylinder and into the reservoir. In the opposite direction of movement of the cylinder, there is more fluid moving away from the cylinder and into the reservoir, than there is moving towards the cylinder and out of the reservoir. Accordingly there must be provision in such a reservoir to accommodate different levels of fluid which arise when the cylinder moves in different directions. Typically this is done by providing a vented reservoir. These are undesirable for some applications due to the possibility of contamination or loss of fluid through the vents. In theory an air space could be left in the reservoir to allow for additional fluid. However there is typically nothing to stop the user from overfilling the reservoir and reducing or eliminating the air space such that the reservoir can no longer accommodate additional fluid.
Accordingly it is an object of the invention to provide an improved hydraulic fluid reservoir which is configured so as to give an accurate fluid level reading to a photodetector.
It is another object of the invention to provide an improved hydraulic fluid reservoir which can be unvented, but yet reliably accommodate different volumes of fluid.
It is a further object of the invention to provide an improved combination hydraulic pump and reservoir which is rugged in construction, reliable in operation and economical to produce and sell.